程序中父子进程分别在自己的一个窗体中显示，第一次按tab键可以从父进程窗体切换到子进程窗体，再次按下tab键之后，程序已经且到父进程窗体，但是没有刷新出父进程窗口以前输入的东西。请问是怎么回事？是不是跟父子进程通过信号通讯有关，我去掉信号写的测试程序都可以相互之间切换啊？
   代码如下：
#include 
#include 
#include 
#include 


void initcurses();
void initwin(WINDOW **wins,int k);
void cov(WINDOW **win,int i,int ch);
void tell_wait();
void wait_child(void);
void wait_parent(void);
void tell_child(pid_t pid);
void tell_parent(pid_t pid);
void sig_usr(int signo);

static volatile sig_atomic_t sigflag;
static sigset_t newmask, oldmask, zeromask;


main()
{
    int ch,i=1,j =0 ,k=2;
    int start=0;
    int exit=0;
    WINDOW *wins[2];
    pid_t pid;

    initcurses();
    initwin(wins,k);
    box(wins[0],'.',',');
    box(wins[1],'!','#');
    touchwin(wins[0]);
    wrefresh(wins[0]);

    tell_wait();
    while (ch = wgetch(wins[0]))
    {
        switch(ch)
       {
            case 'q':
                  exit = 1;
                  break;
            case 9:
               if (0 == start)    //第一次切换
                 {
                    if ((pid = fork()) == 0)    //子进程
                       {
                          touchwin(wins[1]);
                          wrefresh(wins[1]);
                          while(ch = wgetch(wins[1]))
                            {
                               switch(ch)
                                 {
                                    case 9:
                                        exit = 1;
                                        break;
                                    default:
                                        cov(wins,1,ch);
                                        break;
                                 }
                               if (1 == exit)
                                 {
                                    tell_parent(getppid());
                                    wait_parent();
                                 }
                            }
                       }
                     else if(pid >0)            //父进程
                       {
                          wait_child();
                          start = 1;
                       }
                 }
               else
                 {
                  exit = 1;   // 第二次由父进程切回来自动退出
            }
                 break;
            default:
                 cov(wins,0,ch);
                 break;
        }
        if (1 == exit) break;
        touchwin(wins[0]);
        wrefresh(wins[0]);
mvwaddstr(wins[0],3,4,"222222");
wrefresh(wins[0]);//再次切换到父窗体的时候，会显示22222但是为什么边框仍然为子窗体的边框

     }

   endwin();
}

void initcurses()
{
    initscr();//初始化curses库
    noecho();
    keypad(stdscr,TRUE);
    box(stdscr,'┃','━');
    refresh();
}

void initwin(WINDOW **wins,int k)
{
    int i;

    for(i = 0;i